In recent years, the proportion of using a full-section tunnel boring machine (TBM for short) for mechanical construction in tunnel construction is higher and higher; and the full-section TBM is a novel and advanced tunnel construction machine excavating by virtue of a rotary tool, and breaking surrounding rock in a tunnel and tunneling meanwhile, so as to form a whole tunnel section. When the TBM is used for tunneling, a prominent problem that the TBM is poor in adaptability to the changes of geologic conditions exists, so that serious accidents of blockage, burying and even mechanical scrap of the TBM are usually caused in unfavorable geologic conditions of faults, crushed zones, lithologic interfaces, water-bearing structures and the like. In order to reduce the risk of encountering the accidents aforementioned in TBM construction, the most effective solution is to detect unfavorable geologic conditions ahead of a working face in advance by adopting an advanced geologic forecast technology, and formulate a reasonable disposal measure and a construction plan in advance according to the geologic conditions ahead of the working face.
However, a very mature and effective special advanced geologic forecast method for a TBM construction tunnel is inexistent at home and abroad presently. For advanced geologic forecast devices and technologies, TBM construction has essential differences relative to drilling-blasting method construction: (1) the TBM is huge and occupies most of space behind the working face of the tunnel, and a common induced shot point and a common reception system for advanced forecast using a seismic wave method can not be arranged at the side wall of the tunnel, so that common advanced forecast technologies using the seismic wave method, such as TSP, TGP, TRT and the like in drilling-blasting method tunnels can not be applied to the TBM construction tunnels; (2) lots of metal members and power supply cables existing in the TBM are great in interference on an electromagnetic field, so that general advanced geologic forecast technologies based on an electromagnetic principle, such as a geologic radar method, a transient electromagnetic method and an induced polarization method, are extremely unsatisfactory in detection effect, and then can not be applied to the TBM construction tunnels; and (3) during TBM construction, about two hours of machine overhaul time should be ensured every day; and when the machine is overhauled, the cutter head of the TBM retreats 2-5 m, the narrow space can be used for implementing advanced geologic forecast, and the space is narrow and short in available time.
For the existing advanced geologic forecast technology in the TBM construction tunnels, two methods are mainly provided: (1) horizontal drilling is performed by virtue of an advanced drilling machine equipped by the TBM; and the drilling machine is only capable of showing the surrounding geologic conditions of a drill hole, incapable of detecting geologic bodies which are not intersected with the drill hole and reflecting the geologic conditions in the whole range ahead of the working face of the TBM, extremely easy to miss unfavorable geology to cause false alarm, wrong alarm and disaster hidden dangers, as well as high in economic cost and time cost for drilling. (2) a BEAM (Bore-Tunneling Electrical Ahead Monitoring) system researched and developed in Germany is used, and BEAM is a one-dimensional focusing-type induced polarization method; and the BEAM method has the following defects: 1, test equipment is complex in installation, and test time is long, so that construction progress is seriously influenced; and 2, in the BEAM method, the water-bearing condition ahead of a tunneling face is deduced by virtue of the measurement result of every time and the curve of a tunnel mileage, the detection distance is short, and tomography detection is not used, so that the three-dimensional information of geologic bodies ahead of the working face of the TBM can not be obtained, and water quantities can not be forecasted as well. In addition, from the view point of the application conditions of the BEAM method in a few of tunnels in China, the forecast result is unsatisfactory, and the BEAM method is not popularized and needs to be improved and perfected.
Thus it can be seen that very effective and practical advanced geologic forecast technology and device are inexistent for a TBM construction tunnel presently due to the reasons of narrow detection space, great electromagnetic interference, short available time and the like.